Electrostatic dust precipitator



July 19, 1949. c. w. PENNEY ET AL 0 ELECTROSTATIC DUST-PREC IPITATOR Filed Nov. 6, 1947 2 Sheets-Sheet 1- WITNESSES: INVENTORS d I Gay/0rd M Penne y an GecgIY'ye M Hewi/f. fiw. A.

ATTORN EY July 19, 1949.

G. w. PENNEY ETAL 2,476,903 ELECTROSTATIC DUST-PRECIPIIATOR Filed Nov. 6, 1947 2 Sheets-Sheet 2 INVENTORJ Gdy/ord/V. Pen/n y and George M fiew/ff.

ATTORNEY Patented July 19, 1949 ELECTROSTATIC DUST PRECIPITATOR Gaylord W. Penney and George W.

burgh, Pa.,

Corporation, East Pit tion of Pennsylvania Hewitt, Pittsassignors to Westinghouse Electric tsburgh, Pa., a corpora- Application November 6, 1947, Serial No. 784,330

8 Claims.

Our invention, in a sense, relates to an electrical gas-cleaning dust-precipitator of a type having an electrical ionizing means through which dust-carrying gas is passed for electrically charging or ionizing the gas-borne dust-particles. In a broad sense, our invention is directed to improvements in electrosatic dust-precipitators of a type comprising an upstream ionizing means, or ionizer, and a downstream dust-precipitatin means which, preferably but not necessarily, comprises a plurality of closely spaced, alternately oppositely charged, parallel plates.

The function of the ionizer is to produce a concentration of ions of one sign or potential-polarity only in a space through which the gas to be cleaned passes so that gas-borne dust-particles will become ionized and can be subsequently electrostatically precipitated in the downstream dustprecipitating means. A form of such a dustprecipitator, to which, however, our invention is not limited, is disclosed in Penney Patent No. 2,129,783 of September 13, 1938.

The customary ionizer comprises a, plurality of spaced parallel cylindrical non-discharging electrodes and discharging electrodes which extend transverse to the direction for gas-flow therebetween and are relatively insulated. The former are relatively large as compared to the latter which usually are relatively fine ionizing wires. A comparatively low unidirectional voltage is usually connected between the relatively large electrodes and the fine wires, although higher voltages have been suggested. As disclosed in the aforesaid Penney patent, the ionizing wires should be relatively fine and usually less than about 32 mils in diameter in order to provide adequate ionization without significant production of harmful gases such as ozone or oxides of nitrogen. In a practical embodiment about 12,000 to 14,000 volts is used across a 5 mil wire and a cylindrical electrode of about 1 inch outside diameter which is spaced about 1 inches from the wire.

When such ionizers are used for cleaning gas, especially a dry gas containing dust-particles of a high electrical resistivity, a dirt layer or coating forms on the relatively large electrodes. The dirt layer or coating on the non-discharging electrodes may consume a significant portion of the voltage which is across the relatively insulated ionizer-electrodes. It seems that this coatingvoltage sometimes punctures the dirt layer or provides high voltage-gradients at sharp points of the coating or dirt on the relatively large electrodes. Electrical discharges may thus result that tend to neutralize or oilset, at least to some extent, the ionization provided by the ionizing wires. Whatever its cause, this phenomenon is more generally known as back-ionization and is characterized by a secondary or additional discharge at or near the surface of the erstwhile non-discharging relatively large electrodes, which generates ions having an electrical charge of a polarity opposite to that provided'by the ionizing wires. Back-ionization may seriously interfere with the design and operation of an electrostatic dust-precipitator. A dirty relatively large electrode at which back-ionization is present, causes a decrease in the air-cleaning efliciency of the dust-precipitator, has a tendency to increase vibration of the ionizing wires, and may also cause excessive generation of ozone and other obnoxious gases.

It is an object of our invention to provide an ionizer of a type described in which back-ionization is reduced or minimized.

It is an object of our invention to provide a relatively high-voltage ionizer of a type described using fewer electrodes for a given gas-cleaning rating.

It is a further object of our invention to provide an ionizer having a special advantage for use in electrical dust-precipitators required to remove high-resistivity dust-particles from a comparatively dry gas or a gas having a relative humidity in the neighborhood of 25 per cent or less.

An important object of our invention is to provide an ionizing means of general utility in which each non-discharging electrode is uniformly coated with an oily liquid, so that the dirt on all parts of the electrode is wetted with the result that the layer or coating tends to be of more uniform electrical resistivity. In any event, the liquid seems to fill up the spaces between dust-particles on the electrode, and minimizes the conditions which give rise to backionization. The liquid-coating nullifies the tendency of a thin layer of dirt on the electrode to produce back-ionization. With a, dry surfaced electrode, even an extremely thin dirt layer is troublesome with respect to back-ionization. Hence a dry electrode must be kept very clean for satisfactory operation, whereas a liquid coated electrode need not be cleaned so thoroughly for satisfactory operation.

An electrostatic dust-precipitator in accordance with a preferred form of our invention comprises an ionizer and a dust-precipitating means arranged successively in the direction of gas flow. The ionizer comprises a plurality of rela tively large cylindrical non-discharging electrodes which can be "rotated about a vertical central axis. A jet of liquid is periodically applied to the top surface of each such electrode while it rotates, for the purpose of cleaning and of ooating the electrode with liquid.

The quantity of liquid is preferably limited, ant

as applied does not cover the entire surface of the electrode; but a means in the form of a scraper or spreader bears on the rotating electrode surface for spreading :theiliquid completely over the surface of the electrode, so that the small quantity of liquidis usually adequate for both cleaning and coating. The combined action of the liquid and scraper or spreader seems to loosen the dirt on the electrode and pile it up at the forward edge of the scraper or spreader. The piled-up liquid :and dirt mixture is sufficiently liquidy or fluent to flow downwardly into any suitable collecting trough. in inven tion, the scraper oris'preader distributes or spreads the wetting liquid over the surface of the elec= trode, but does not scrape all of the liquid from the surface. A thin filmof liquid remains which seems to have a wetting and filling action subsequently collected :dirt. Whatever the action of the film of liquid may .be, any dirt which initially deposits on the coated electrode becomes well wetted and is less likely to cause backicnization. Moreover, the wetted dirt at the surface of the electrode makes it easier to scrape off excess dirt from the electrode when the electrode is again treated; Hence, our system .cornnines the use ofa wetting liquid and a scraper or spreader, as distinguished from the separate use of a liquid flushing alone or a scraper alone and for cleaning only, as suggested, for exam ple, in ll ieston Patent No. 1,9036%, .01? April '11, 1933.

Other objects, features, innovations, methods and structures .of our invention be discernible from the followingdescription-of a preferred form thereof which is :to be taken in conjunction with the accompanying drawings, not to scale,

in'which:

Figure 1 is a diagrammatic view through a horizontal gas-duct having an electrostatic dustprecipitator built generally in accordance with our invention;

Fig. 2 is a broadside elevational view of an ionizing means in accordance with our invention, with parts broken away for more clearly showing other parts of the structure;

Figs. 3 and :4 :are sectional views taken sub stantially along the lines .IifI ilIi and IV-IV of Fig.2 respectively; .and

Fig. 5 is a wiring diagram of electrical loonnections which can be used for controlling the equipment disclosed in the foregoing figures.

Referring more particularly :to Fig. l, a gas duct 2 is shown in which :a gas-flow is established in the direction of :the arrow A by a blower means ill-which includes an electric motor 6. .A gas-cleaning electrostatic :dust-precipitator is arranged in the gas-duct 2 and comprises an upstream ionizing means or ionizer 8 in which gasborne dust-particles receive an electric charge, and a downstream dust-precipitating means ID in which charged dust-particles are removed from the gas-stream.

In common with other similar ionizing means, the ionizer 8 comprises a frame which supports a plurality of spaced relatively large, cylindrical or curved electrodes between which discharging electrodes or ionizing wires can be located. As shown in Figs. 2-4, the frame comprises a plurality of flat parallel bars II and l2 secured to the end portions of comparatively flat legs [3 of a pair of spaced U-shaped bars I l and is which form opposite sides of the frame. The U-shaped bars I4 and I5 have comparatively long flat bases 15 which lie in a plane perpendicular to the planes of the bars II and I2. A transverse flat central cross-bar I1 is secured to the center portions of the bases Hi. In its preferred use, the ionizer 8 is placed with its electrodes upstanding so that the bar ll comprises a horizontal upper bar and the bar l2 a horizontal lower bar; and the spaced bases l6 are upright.

Rotatably supported at equally spaced points along the lower bar 12 is a plurality of short metal shafts 18 which position ends of rods as which constitute the relatively large cylindrical electrodes of the ionizer. While a tube-which is a cylinder having circles as bases provides the most economical electrode, our invention is not limited to such construction, the term cylindrical being intended to embrace any rod having curved bases which are not necessarily exact circles. The cylindrical tubes .20 constitute non-discharging electrodes, by non-discharging meaning that the field gradient intended or desired at the surface of an electrode is insufficient to provide an elec trical discharge or emission therefrom when the surface is free from dirt. Such non-discharging electrodes are sometimes identified for convenience las uninsulated or ground electrodes because they are usually a convenient reference point for electric potentials, actual ground generally being such a pcintbecause of safety and other con siderations. Accordingly, any reference to such electrodes as ground or uninsula-ted electrodes is intended to be :a convenient identification thereof.

The upper ends of the cylindrical electrodes 29 have short rotatable metal shafts 22 secured thereto which pass through any suitable metal guide and thrust bearings fastened to the upper bar ill. The shafts l8 and 22 :can be remo'va'bly secured to the electrodes 2!] in any suitable manner as, for example, by fixin a metal sleeve as :in each .end and providing each sleeve with a hole for receiving a setscrew 26 for fastening the associated end .of the electrode to the associated shaft.

6n the topside of the upper bar H, each rotatable-shaft 22 is providedwith asprocket wheel 28. The wheels 28 mesh with a sprocket chain 35. One of the shafts '22 may be providedwith a second sprocket wheel 3| driven :by a sprocket chain (Fig. 11) which, in turn, is driven, through any suitable gearing, by .an electric motor 33 whenever the motor is electrically energized. Preferably the sprocket chain 39 meshin with the sprocket wheels 28 .is so arranged that the wheels on "the consecutive electrodes 20 rotate in opposite directions, as indicated by the arrows B and C in Fig. 3.

Associated with each of the rotatable cylindrical electrodes 2,!) is a device which functions both as a scraper and as a liquid spreader or distributor. Each of these devices comprises a scraper bar comprising a flat resilient strip 34 of phosphor bronze, which lightly presses axially against the associated electrode at for substantially the full length thereof. Preferably, the sharp edge of the strip is slightly above the clot trode-surface; but the side of the strip 34 is against the surface with the edge very close to the line of contact. The scraper strip 34 has its other edge reinforced by narrow rigid bars 35 having end lugs 36 which are fastened to the frame-bars H and I2.

Periodically, a liquid, preferably but not neces= sarily one of good insulating qualities and low vapor pressure, is fed to the tops of the cylindrical electrodes 20. To this end, liquid discharger means is provided comprising short jets or nozzles 37 connected to a common supply pipe or manifold 38, and through which liquid can be discharged to the tops of the electrodes. Preferably, the liquid is supplied while the electrodes 28 are being rotated.

In accordance with our invention, discharging or ionizing wires are supported from the frame so that there will be no interference with the rota= tion and cleaning of the cylindrical electrodes 2%. To this end, a U-shaped bracket 39, considerably smaller than the U-shaped bars i5 and I5, fastened to the center part of the central crossbar 7, with the base of the bracket to paralleling the bases is of the U-shaped bars Id and :5, but located midway between them. The bracket 33 has legs id to the ends of which outwardly extending insulators 4| are secured. The other or far end of each insulator has an elongated metallic angle bar 132 secured thereto which extends per pendicular to the electrodes 26 but is insulatedly spaced therefrom. Each bar 42 carries metal arms 43 which are directed toward the transverse center of the spaces between each pair of electrodes 2%. An ionizing wire 43 is longitudinally strung in each such space, being fastened to aligned opposite arms 43. In the embodiment shown in Figs. 2-4, there are four such spaces re quirin' four ionizing wires.

The bottom of the frame is provided with plate parallel to and abutting the edge of the lower bar 42. Preferably this plate and the bar I: slope slightly so that liquid can readily drain therefrom.

In the embodiment disclosed, the dust-precipitating means it comprises a plurality of relatively insulated plate-type dust-collecting electrodes 28 and 5% which are closely spaced so as to provide a suitable dust-precipitating electrostatic field be tween each pair of consecutive plates, as more fully described in the aforesaid Penney patent.

For gas cleaning, a unidirectional voltage, de rived from a voltage conversion means or power pack, is connected across the ionizing Wires 44 and the relatively large cylindrical electrodes 26 and a unidirectional voltage is connected across the relatively insulated electrodes 48 and 59. Referring to Figs. 1 and 5, a power pack 52 applies a high positive potential to aninsulated conduc tor 5% connected to an insulated bar 12 for charg ing the ionizing wires, and to an insulated conductor it connected to a metal support for the plates 48. The electrodes 2G and the other plates 53 are preferably grounded so as to complete circuits to the grounded conductor 58 of the power pack 52.

In operation of the apparatus described for cleaning air, the ionizing wires 44 are preferably positively charged and provide an ionized electrostatic field in the spaces provided by the electrodes of the ionizer 8. The ionizing electrostatic field is intended to function solely for charging dust-particles in a gas flowing past the electrodes so that such dust-particles will be electrostatically precipitated as they pass between the oppositely charged plates 48 and 59. However, in many instances, there is a tendency for some of the dust-particles to precipitate on the cylindrical electrodes 29 and form a dirt deposit thereon of high resistivity.

In accordance with our invention, the electrodes 2%) are kept clean and coated in an inexpensive but satisfactory manner by applying a small stream of a suitable liquid to a point near the top of each electrode while the electrode rotates against its associated dirt-scraping and liquid-distributing device comprising the scraper bar having the scraper strip 34%. The liquid is supplied to the tube through the discharge nozzles 3?, being pumped to the manifold 38 by a pumping system comprising a pump to which takes oil from a reservoir 62 when the pump is driven by an electric motor 54.

Preferably the liquid should be of an oily pene= trating natiue. A great many liouids of this kind are known and would be satisfactory if the only considerations Were the wetting and coating properties of the liquid. However, other characteristics usually make it necessary to discard an otherwise utilizable liquid. Obviously, it is not safe or desirable to use a liquid in an ail -cleaning electrostatic dust-precipitat 1', which, for example, is highly volatile, is highly flammable, or decomposes or changes quickly under electric stress, or has a toxic vapor phase, or oxidizes readily. Suitable liquids, to which our invention. is not limited, that may be used are good grade motor oils. As an example, .5. A. E. 10-20 has been found satisfactory. Liquids consisting en tirely or mostly of tricresyl phosphate are, as a rule, also satisfactory. Chlorinated diphenyls are also utilizable. Hereinafter such suitable liquids are designated as oils or oily liquids.

During rotation of each cylindrical electrode 2!] a small jet of liquid'is adequate because the strip 3 scrapes and loosens any dirt that may be tenaciously stucl: to the electrode, also mixes the liquid with the dirt on the electrode. Each scraper strip 34 should have an edge which is Wide enough to act as a sort of dam for some of the mixture of liquid and dirt which it scrapes off the electrode. The liquid is preferably supplied in such small quantity that a syrupy mix-- ture of liquid and dirt, in the form of a sludge, piles up at the strip-edge, which slowly migrates downwardly along and near the strip-edge to the sloped bottom of the ionizer and then into a trough 65 connected by a pipe 58 to th reservoir 82, where the sludge may be cleaned. After the rotation of the electrodes 29 is stopped, what ever excess liquid may be on the electrode-surface will slowly drain.

The strip 3 bears so lightly on the electrode that a thin film of liquid remains over the whole surface of each electrode, although a small quantity only of the liquid has been applied to it, and at a single point on its surface. Absolute cleanliness of the electrode surface is not essential in order to limit back-ionization, and the liquid film left on the electrode can be dark, if desired, rather than clear.

Flushing of the electrode with large quantities of liquid is not necessary for attaining the objectives and advantages of our invention; By flushing we mean delivering such quantities of liquid over the entire surface at such force that the lio uid will wash the dirt oil the entire electrode and carry it down into a trough, such without the aid of a scraper, such as strip 3 5.

There are no particularly exactlimitations for the rate at which the liquid must be applied to each electrode. It should not be so small as to prevent the strip 34 from spreading or distributing the oil completely over the surface of the electrode, but it need not be in such great quantity as to wash down the electrode without the aid of the strip. However, the rate should be sufiicient to provide enough liquid to carry the dirt down at least at and near the edge of the strip where it accumulates, that is, piles up; The linear velocity of the electrode-surface need not be high. On the contrary, it is preferably low, and considerably below a value at which centrifugal action would disturb the liquid thereon. A thin film or coating remains on the cylindrical electrodes 29 after they have been scraped. The liquid should be of low volatility so that it does not evaporate from the surface of the electrode between electrode-treatments.

The periods during which the cylindrical electrodes 2d are cleaned, preferably by the simultaneous rotation of the electrodes and the application of liquid, need not be very long and can be spaced apart a relatively considerable length of time. For example, treating the elec rode by combined scraping and liquid-application for about eight minutes to one hour or more from two to three times a day or even less has been found satisfactory with ordinary atmospheric dust of the type found in Pittsburgh, Pennsylvania, during the winter time,

A simplified control which can be used for operating the apparatus in a particular manner is shown in Fig. 5. Electric power supply conductors is energize a timer motor M which drives a cam 14. The cam M completes one rotation during the time-interval desired between cleaning periods and maintains a time-operated switch re closed substantially for the length of such period. When the switch 16 closes/it energizes a first relay it; which is quick to actuate but slow to release, and a completely quick acting relay 80.

When the relay is instantly actuates, it opens its contacts 82 and thereby interrupts an energizing circuit 84 for the energizing motor ii of the blower means ii, and interrupts an energizing circuit 88 for the power pack 52. Accordingly, the gas-flow through the gas-duct 2 ceases high-voltage is removed from the electrodes is and d8 of the dust-precipitator. When the relay EB actuates, it also closes contacts 05 for completing a circuit 92 to the motor 33 which thereupon rotates the cylindrical electrodes 20.

Energization of the relay ill! instantly closes contacts 94 which complete a circuit 90 to the pump motor 6 Accordingly, liquid is supplied to the top of the electrodes 20 by the pump 5d while the electrodes are rotated by the electric motor 33.

After a time, the timer switch It opens and causes the relays 18 and B0 to be deenergized. The contacts as of the relay at open instantly and deenergize the pump motor 64 so that the flow of liquid to the electrodes Zii ceases. However, deenergization of the relay iii does not immediately close its contacts 82 and open its cont'acts 90 because the relay 118 is of the time delay release. However, after this release time, the contacts as separate and the electrode-rotating motor 33 becomes deenergized so that the electrodes 20 cease rotating. At the same time, the contacts 82 close, re-establishing the gas-flow through the gas-duct 2, and reapplying highvoltage to the insulated electrodes of the dustprecipitator. The time delay required for the relay is to release its contacts is adjustable, and during this time the electrodes rotate without oil being applied to them. This means that the remaining oil on the electrodes is more evenly and thinly spread over their surfaces.

Although the relay [8 has been described as operating with adelayed release, the release time may be made zero so that the relay operates simultaneously with the relay 80. Under this condition the liquid-application and rotation of the electrodes are concurrent.

In the control described, voltage is removed from the electrodes and the blower is stopped during treatment of the electrodes. This scheme is recommended when the treating periods are short and a liquid is used of comparatively poor insulating qualities. However, the blower and electrodes may remain energized during the treating periods. To this end a circuit including manually operable switch 94 is provided across the contacts 82. By closing this switch 94, the motor i5 and power pack 52 remain in operation while the electrodes rotate and liquid is applied to them. In other words, there is no interruption of the electrostatic gas-cleaning.

By keeping each cylindrical electrode 20 relatively clean and oiled in the manner described, the conditions for back-ionization are made so poor that it is possible to use a comparatively higher voltage between the ionizing wires 14 and the electrodes 25, and. to increase the spacing between them. It is also advantageous, under such conditions, to increase the diameter of the ionizing wires so that they will be stronger. A further result, stemming from the use of higher overall voltage, is that the voltage drop across any liquid and dirt film on the electrodes is a smaller fraction of the total voltage across the electrodes. For example, if the voltage drop across a dirt layer is 2,000 volts, this value constitutes of an overall voltage of 12,000 volts between the relatively insulated electrodes of an ionizer, but only /10 of an overall voltage of 22,000 volts between similar electrodes. This means that the dirt layer under the latter condition will not afiect the discharge current from the ionizing wires as much as under the former condition.

Instead of 5 mil Wires, or thereabouts, currently used in ionizers of the type described, the wires may be larger and hence more rugged. Fifteen mil wires have been found satisfactory for an ionizer in which the ionizing wires were spaced 2 /8 inches from the surface of its associated non-discharging relatively large electrodes. In such an ionizer a voltage of 22,000 volts was successfully applied to the relatively insulated ionizer-electrodes without excess ozone or other gases. For a given gas-duct area and gas-velocity, the result is that fewer wires will be needed to charge the gas-borne dust-particles. In such an embodiment of our invention, to which we are not limited, a relatively large electrode 1%, inches in diameter and 30 inches long and rotating at 36 revolutions per hour (about R... P. M) was kept satisfactorily clean with 'S, A. E. oil supplied at a rate of one-half pint per minute during rotation of the electrode.

While we have described our invention in a form now preferred, it is obvious that it is sublect to wide variations and modifications without departure from its principles and teachings. An ionizing means of a type herein described is incorporated in the gas-cleaning system disclosed and claimed in our copending application, Serial No. 603,503, filed July 6, 1945, and entitled Precipitator, now Patent No. 2,448,046, dated August 31, 1948, This application is a continuation in part of our application Serial No. 603,504, filed July 4, 1945 and entitled Ionizing means, now abandoned.

We claim as our invention:

1. An ionizing means of a type described comprising, in combination, an open frame, a pin-- rality of spaced elongated cylindrical electrodes rotatably supported by said frame, means comprising an electric motor and gearing for rotating each of said cylindrical electrodes about a longitudinal axis, a plurality of scraper bars cured to said frame, there being a scraper bar for each of said cylindrical electrodes, an ionizing wire for each space provided by said cylindrical electrodes, means for insulatedly supporting said ionizing Wires in discharging relation to said cylindrical electrodes, liquid-discharger means carried by said frame for directing liquid to each of said cylindrical electrodes, means comprising a pump and an electric motor therefor for supplying said liquid-discharger means with liquid, and an energizing circuit including switching means for periodically temporarily having both said electric motors simultaneously deenergized, said switching means bein operable for energizing said electric motors.

2. A unitary structure for an ionizing means of a type described, comprising, in structural combination, a plurality of spaced elongated parallel upright cylindrical electrodes; an ionizing wire for each space provided by said cylindrical electrodes; means for insulatedly supporting said ionizing wires in discharging relation to said cylindrical electrodes; means for directing a gas between said spaces in a direction transverse to said electrodes; and electrode-cleaning means comprising a scraper means for each cylindrical electrode, mechanical means operable for relatively moving each said cylindrical electrode and its associated scraper means, limitedquantity liquid-dispensing means operable for supplying liquid to the top of each cylindrical electrode, and power means for operating said mechanical means and said liquid-dispensing means,

3. Ionizing means of a type described comprising a metallic frame having a pair of sides and a, cross-bar extending therebetween, a plurality of spaced elongated cylindrical electrodes rotatably supported in parallel spaced relation by said sides, an ionizing wire for each space provided by said cylindrical electrodes, a U-shaped bar secured to said cross-bar, outwardly extending insulators secured to the legs of said U-shaped bar, and bar means secured to each of said insulators, said bar means includin arms extending into said spaces for supporting said ionizing wires in insulated discharging relation to said cylindrical electrodes.

4. A unitary structure for an ionizer of a type described, comprising: a plurality of spaced elongated relatively insulated parallel cylindrical electrodes, a first of said electrodes being relatively large and a second of said electrodes comprising a discharging electrode outwardly away from said first electrode in discharging relation thereto; in combination with means for rotating said firstelectrode about a longitudinal axis, limitedquantity liquid-dispensing means for applying a liquid to said first electrode while it is being rotated, and a liquid-spreader pressing on the surface of said electrode for spreading liquid thereover.

5. Ionizing means of a type described comprising, in a structural combination,'a plurality of spaced elongated parallel cylindrical electrodes, means comprising jet-nozzles adapted to discharge a liquid on the surfaces of said cylindrical electrodes, electrode-treating and cleaning means comprising a liquid-spreading dirt-scraper means constructed and arranged for'relative movement across said surfaces of said electrodes, a discharging electrode in each space provided by said spaced cylindrical electrodes, means for insulat edly supporting said discharging electrodes in discharging relation to said cylindrical electrodes, and means for simultaneously supplying said jetnozzles with liquid, and for relatively moving said cylindrical electrodes and said liquid-spreading and dirt-scraper means.

6. Ionizer means of a type described comprising in a structural combination, an open frame through which gas may flow, an elongated parallel cylindrical electrode rotatably supported by said frame, gearing for rotating said cylindrical electrode about a longitudinal axis, an elongated scraper for said cylindrical electrode, comprising a resilient member pressing lengthwise against said cylindrical electrode, an ionizing wire in discharging relation to said cylindrical electrode, and a jet-nozzle attached to said frame for applying a liquid to a part only of the surface of said cylindrical electrode, said scraper being arranged to spread the liquid over the surface of said cylindrical electrode when it is rotated.

7. Electrostatic apparatus of a type described comprising, in combination, a gas-duct, draftinducing means providing a draft through said gas-duct, an ionizer in said gas-duct, comprising an open frame, a plurality of spaced elongated cylindrical electrodes rotatably supported by said frame, means comprising an electric motor and gearing for rotating each of said cylindrical electrodes about a longitudinal axis, a plurality of scraper bars secured to said frame, there being a scraper bar for each of said cylindrical electrodes, an ionizing wire for each space provided by cylindrical electrodes, means for insulatedly supporting said ionizing wires in discharging relation to said cylindrical electrodes, liquid-discharger means carried by said frame for directing liquid to each of said cylindrical electrodes, means comprising a pump and a second electric motor therefor for supplying said liquid-discharger means with liquid, and an energizing circuit including switching means for periodically temporarily having both said electric motors simultaneously deenergized, and for energizing said electric motors while said draft-inducing means provides a draft through said gas-duct.

8. A method for keeping an ionizing means in operating conditions, the ionizing means comprisin a plurality of spaced ionizing electrodes and non-discharging elongated upstanding cylindrical electrodes cooperating to form an ionized electrostatic field, said electrodes being transverse to the direction of gas-flow therethrough, said method comprising periodically rotating eubstantmny ccmp'letciyccat the surface of each 10 cylindrical electrode a,n d to render the dirt-depesit 6Y1 'fi lfitiii'gl feijljgehp. M V

GEORGE W. HEWITT.

, ITED The are of record in the me at this patent:

Number 12 UNITED STATES PATENTS V Name Date Girvin Jan. 1, 1918 Merton Apr. 11, 1933 Brossert Feb. 20, 1934 Merton Mar. 9; 1934 FOREIGN PATENTS Country Date Number Germany Aug. 3; 1924 Germany July 15, 1929 Germany ...1 June 24, 1932 Germany Dec. 7, 1938 France Dec. 14, 1926 

